Milling insert

ABSTRACT

A milling insert, including an upperside, an underside, and a reference plane parallel thereto. A plurality of indexable cutting edges are formed along a peripheral borderline in transitions between at least the upperside and a number of clearance surfaces. Each cutting edge includes a chip-removing main edge and a surface-wiping secondary edge. The main edge, from a first end of the main edge adjacent to the secondary edge, declines toward the underside of the milling insert and then, from a lowest part, rises toward an opposite second end of the main edge. The secondary edge is inclined at an angle (ε) in relation to the reference plane as viewed perpendicularly to the clearance surface of the secondary edge, such that a first end of the secondary edge connected to the main edge is situated on a lower level than the opposite, second end of the secondary edge.

This application claims priority under 35 U.S.C. §119 to Swedish PatentApplication No. 0801075-3, filed on May 13, 2008, which is incorporatedby reference herein in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to a milling insert of the typethat includes an upperside, an underside, a reference plane parallel tothe same sides, and a number of alternately applicable cutting edges,which are formed along a peripheral borderline in transitions between atleast the upperside and a number of clearance surfaces, and whichindividually include a chip-removing main edge and a surface-wipingsecondary edge, which—as viewed in planar view—forms an obtuse anglewith the main edge. The main edge of the individual cutting edge, from afirst end adjacent to the co-operating secondary edge, first declinestoward the underside of the milling insert and then, from a lowestpoint, again rises toward an opposite end.

The invention is particularly suitable for and advantageous inconnection with double-sided milling inserts for face milling, i.e.,milling inserts, the uppersides and undersides of which are identical inrespect of the insert geometry and individually include three or morecutting edges being alike, which are alternately applicable by indexing(rotation) of the milling insert.

BACKGROUND OF THE INVENTION

Milling tools for chip removing machining of, above all, workpieces ofmetal (steel, aluminum, titanium, etc.) are generally composed of arotatable basic body or milling-cutter body, most often of steel, aswell as a plurality of replaceable milling inserts of cemented carbide,ceramics or the like. Because the milling inserts are expendablematerials as a consequence of being worn fairly fast, it is most oftendesirable to form the same with as large a number of cutting edges aspossible. For this reason, the milling inserts may be carried outdouble-sided so far that the underside is formed with the same number ofcutting edges as the upperside, while doubling the number of cuttingedges in comparison with single-sided milling inserts. Therefore,milling cutters for face milling are often equipped with milling insertsthat are double-sided and have a quadratic basic shape with four cuttingedges, i.e., four pairs of co-operating main edges and secondary edges,along the upperside as well as the underside, and which are mounted atan effective setting angle of approximately 45° in the milling-cutterbody. In such cases, the main edge and the secondary edge form a nominalangle of 135° with each other.

The problems forming the basis of the present invention are associatedwith double-sided face milling inserts of the type that is denominated“negative,” and which are formed with clearance surfaces that extendperpendicularly to the neutral plane to which the uppersides andundersides are parallel. In order to provide requisite clearancebetween, on one hand, the clearance surface present (rotationally)behind the active, surface-wiping secondary edge, and on the other handthe generated, plane surface of the workpiece, the milling insert has tobe mounted with a negative axial tipping-in angle in the milling-cutterbody. Simultaneously, the milling insert also has to have a negativeradial tipping-in angle in order to provide clearance between, on onehand, the clearance surface behind the chip-removing main edge, and onthe other hand the generally cone-shaped surface generated by the same.Just the negative axial tipping in of the milling insert gives, on onehand, rise to greater axial cutting forces than those cutting forcesthat arise when the milling inserts are positively tipped-in, and on theother hand problems with the chip formation as well as the chipevacuation difficult to master, among others so far that the chips tendto be directed obliquely downward toward the generated plane surfacerather than clear from the same.

Before the background of the invention is further described, it shouldbe pointed out that certain fundamental concepts found in this document,e.g., “clearance angle,” can be of either a nominal or an effectivecharacter. When, for instance, a clearance angle is “nominal,” the sameonly relates to the milling insert as such, i.e., without conjunctionwith the milling-cutter body, but if the same is “effective,” referenceis made to the clearance angle that occurs when the milling insert ismounted in the rotatable milling-cutter body and performs chip removal.

The problems caused by the negative axial and radial, respectively,tipping in are particularly accentuated in milling cutters having theolder type of milling inserts, which have a prismatic basic shape andinclude cutting edges, the main edges of which are straight andpair-wise parallel along common clearance surfaces, as well as also thesecondary edges are straight and pair-wise parallel along the commonclearance surfaces thereof. In this case, the main edges will besubjected to particularly great cutting forces and give rise toconsiderable chip formation and chip evacuation problems, because themilling inserts have to be tipped into an equally great negative axialangle, as the desired effective clearance angle between the generatedplane surface of the piece to be machined and the clearance surfacebehind the surface-wiping secondary edge.

More recently, a number of proposal of solutions of the above-mentionedproblems have appeared. Thus, in U.S. Pat. No. 5,807,031, adouble-sided, quadratic face milling insert is disclosed, thechip-removing main edges of which are inclined in relation to theneutral plane of the milling insert, more precisely in such a way thatthe individual main edge, counted from a first end adjacent to theco-operating secondary edge, first declines toward the underside of themilling insert and then, from a lowest point, again rises toward anopposite end. In such a way, the above-mentioned problems are solved ina general way, so far that the effective axial angle of the proper mainedge is reduced from a relatively great negative value to a smaller,more positive value, in spite of the milling insert, per se, (i.e., theneutral plane of the milling insert) has a sufficiently great negativeaxial angle in order to provide the requisite clearance behind thesurface-wiping secondary edge. However, this known milling insert is,nevertheless, associated with a number of shortcomings anddisadvantages. One such disadvantage is that the two secondary edgesalong a common clearance surface of each corner of the milling insertare still straight and mutually parallel. This means that the transitionbetween the individual secondary edge and the appurtenant main edgeforms a fairly sharp corner (as viewed nominally in side view), so farthat the angle between the secondary edge and the declining main edge isconsiderably smaller than 180°. Thus, in the preferred embodiment, thisangle amounts to 165°-170°. Because the corner transition between themain edge and the secondary edge is the part of the milling insert beingabsolutely most exposed to, among other things, forces, heat anderosion, the fairly sharp corner of the same means that the millinginsert becomes fragile and gets a limited service life associated withthe wear thereof. In addition, the wear of such a sharp corner easilygives rise to visible stripes in the finished, wiped-off surface, moreprecisely in the form of shallow, per se, but nevertheless mostdetrimental grooves in the surface being plane in other respects. Inother words, the finish of the generated surface becomes rathermediocre. Another disadvantage is that the peripheral borderline, whichsurrounds the upperside (and the underside, respectively), is a singlecontinuous cutting-edge line. Thus, the cutting-edge line of theindividual main edge transforms directly into an adjacent,non-co-operating secondary edge—or alternatively via diminutive partedges along facet surfaces between the clearance surfaces of the mainedge and the secondary edge—the secondary edges forming the uppermostportions of the upperside, i.e., no other points along the upperside aresituated at a greater distance from the neutral plane than the secondaryedges. This is destructive considering that just the secondary edges arecrucial for the finish of the generated surface, and therefore should besharp or in any case undamaged as long as possible. Because thesecondary edges in the known milling insert stick up in relation to therest of the upperside, the same are subject to miscellaneous risks ofdamage. Thus, damage may easily arise during the handling of the millinginserts, e.g., when the same are placed on metal tables or the like inconnection with indexing and replacements. Because each active main edgedirectly transforms into an adjacent, inactive secondary edge, there is,in addition, a risk that the removed chips hammer against and damage thesecondary edge not yet used. Moreover, the declining or downwardlyleaning part of the main edge, which extends from the co-operatingsecondary edge toward the lowermost point of the main edge, will have alength that is considerably greater than half the length of the mainedge. This means that the material in the milling insert becomesconsiderably thinner in the area of the lowermost point or depression ofthe main edge, whereby the strength of the milling insert is impaired.This detriment will be particularly marked when the milling insertrequires large clearances.

A face milling insert that resembles the milling insert described aboveand which is essentially impaired with the same disadvantages as thesame, is previously described in U.S. Pat. No. 7,306,409.

The present invention aims at obviating the above-mentioneddisadvantages of the previously known milling inserts and at providingan improved milling insert. Therefore, an object of the invention toprovide a milling insert, and in particular a double-sided face millinginsert, the most sensitive parts of which, i.e., the corner transitionsbetween co-operating secondary and main edges are strong and wellfunctioning, in spite of the fact that the main edges of the millinginsert can work with effective rake angles that are moderately negativeor even positive in spite of the effective clearances behind thesecondary edges being ample.

Another object of the invention is to provide a milling insert, in whichthe risk of damage to the sensitive secondary edges is reduced to aminimum.

Yet another object of the invention is to provide a milling insert, inwhich the desired, cutting-technical improvements can be attainedwithout the milling insert being weakened by unnecessary reduction ofthe amount of material (cemented carbide) in the same.

Still another object of the invention is to provide a double-sided facemilling insert particularly suitable for fine milling or semi-finemilling, the main edges of which initially decline at a greater anglethan the remaining parts of the same, in order to, in such a way,additionally refine the qualities of the milling insert in connectionwith fine milling, i.e., milling with small or moderate cutting depths.

SUMMARY OF THE INVENTION

In an embodiment, the invention provides a milling insert, including anupperside, an underside, and a reference plane parallel to the uppersideand the underside. A plurality of indexable cutting edges are formedalong a peripheral borderline in transitions between at least theupperside and a number of clearance surfaces. Each cutting edge includesa chip-removing main edge and a surface-wiping secondary edge, thesecondary edge forming an obtuse angle with the main edge as viewed inplanar view from the upperside. The main edge, from a first end of themain edge adjacent to the secondary edge, first declines toward theunderside of the milling insert and then, from a lowest part, risestoward an opposite second end of the main edge. The secondary edge isinclined at an angle (ε) in relation to the reference plane as viewedperpendicularly to the clearance surface of the secondary edge, suchthat a first end of the secondary edge connected to the main edge issituated on a lower level than the opposite, second end of the secondaryedge.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and constitutepart of this specification, illustrate the presently preferredembodiments of the invention, and together with the general descriptiongiven above and the detailed description given below, serve to explainfeatures of the invention.

FIG. 1 is a perspective exploded view showing a milling tool in the formof a face mill equipped with milling inserts according to an embodimentof the invention;

FIG. 2 is a side view of the basic body of the milling cutterillustrating the axial tipping in of the individual milling insert intothe milling-cutter body;

FIG. 3 is a planar view from below illustrating the radial tipping in ofthe milling insert;

FIG. 4 is a perspective view showing the upperside of the millinginsert;

FIG. 5 is a perspective view showing the underside of the millinginsert;

FIG. 6 is a planar view from above of the milling insert;

FIG. 7 is a longitudinal section VII-VII in FIG. 6;

FIG. 8 is an enlarged side view of the milling insert;

FIG. 9 is an enlarged section IX-IX in FIG. 6;

FIG. 10 is a side view showing the milling insert diagonally in thedirection of the bisector of the individual corner;

FIG. 11 is a detailed view on an enlarged scale illustrating theindividual secondary edge of the milling insert;

FIG. 12 is a partial perspective view of a corner of the milling insert;

FIG. 13 is a partial planar view from above of the same corner; and

FIG. 13B illustrates a magnified view of a portion of a secondary edgeaccording to one embodiment.

FIG. 14 is a schematic section showing the surface structure that can beobtained by a secondary edge having a convex camber.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIGS. 1-3, a milling tool is exemplified in the form of a face mill,which includes a basic body or milling-cutter body 1 and a number ofreplaceable milling inserts 2 (only one of which is shown mounted in themilling-cutter body). The milling-cutter body 1 is rotatable in thedirection of rotation R around a center axis designated C1, andincludes, in a front or lower end, a number of chip pockets 3 for eachone of the milling inserts 2. In the example, the number of chip pocketsamounts to five. The chip pockets 3 are recessed in a rotationallysymmetrical envelope surface 4 and include a seating or insert seat,which is represented by a plane bottom surface 5. Although it is fullypossible to apply the individual milling insert directly against thebottom surface 5, in this case a shim plate 6 is arranged between thebottom surface 5 and the milling insert 2. This shim plate is keptsemi-permanently fixed against the bottom surface 5 by a tubular screw7, in the female thread 8 of which a male thread 9 of a screw 10 can betightened for the fixation of the proper milling insert 2.

As is seen in FIGS. 4-6, the milling insert 2 has a quadratic basicshape and includes four cutting edges 11, each one of which includes achip-removing main edge 12 adjacent to a first clearance surface 13, aswell as a surface-wiping secondary edge 14 (at times denominated “wiperedge”) adjacent to a second clearance surface 15. Because of the millinginsert being double-sided, the same has to be mounted in a specialtipping-in position in the milling-cutter body 1. Thus, in FIG. 2, it isseen how the bottom surface 5, which ultimately determines the solidgeometrical position of the milling insert 2 in the milling-cutter bodydoes not run parallel to the center axis C1, but is tippeddownward/rearward in relation to the center axis C1 as viewed in thedirection of rotation R. In such a way, an effective clearance isprovided between the clearance surface 15 present under, or rotationallybehind, the secondary edge 14 and the plane surface generated andleveled out by the secondary edge 14. In order to, in an analogous way,provide a clearance between the clearance surface 13 of the main edge 11and the cone-shaped surface generated by the main edge, the bottomsurface 5 is furthermore tipped rearward/outward at a radially negativetipping-in angle (see FIG. 3). In order for the clearance of the surface15 to be well functioning, the axial tipping-in angle should amount toat least 4°, but may be greater. In the example, the axial tipping-inangle amounts to 6°, which yields an effective clearance angle α ofapprox. 6° (see FIG. 2). The effective clearance angle α is alsoaffected by the radial tipping-in angle, though marginally. The radialtipping-in angle may amount to 8° or more. The axial and radialtipping-in angles together determine the effective clearance angle βbehind the main edge (see FIG. 3). Suitably, β should be within theinterval of 8°-20°.

It should be pointed out that the milling-cutter body 1 advantageouslyis manufactured of steel or aluminum, while the replaceable millinginserts 2 are manufactured of cemented carbide, ceramics, or othersuitable hard and wear-resistant materials.

Reference is now made to FIGS. 4-13, which in detail illustrate themilling insert 2 only, i.e., without conjunction with the milling-cutterbody 1. The milling insert includes an upperside 16A and an underside16B, the topographic or cutting geometrical design of which correspondswith the design of the upperside 16A. Generally, the upperside and theunderside are parallel to a reference plane RP (see FIG. 8), which inthis case is situated halfway between the same, and which therefore alsoforms the neutral plane of the milling insert. The reference plane RPextends perpendicularly to the center axis C2 of the milling insert,which in this case, when the milling insert is formed with a throughhole 17 for the screw 10, also forms a center axis of the same hole. Aspreviously pointed out, the milling insert has a quadratic basic shapeand includes four cutting edges 11, each one of which includes a mainedge 12 and a surface-wiping secondary edge 14. In FIG. 4, the referencedesignations 11, 12, 13, 14 and 15 are provided with the suffixes a, b,c and d in order to separate an active cutting edge from the inactiveones. The corresponding reference designations in FIG. 5 lack suchsuffixes. Thus, in FIG. 4 the cutting edge 11 a is meant be active, themain edge 12 a and the secondary edge 14 a co-operating with each otherduring the milling operation, while the other three cutting edges,designated 11 b, 11 c, 11 d, are inactive. In FIG. 4, the active mainedge 12 a is shown adjoining an inactive secondary edge 14 b at the sametime as the active secondary edge 14 a adjoins an inactive main edge 12d. It should also be pointed out that in this case, the clearancesurfaces 13, 15 are plane.

In the upperside 16A as well as the underside 16B, a plane surface 18 isincluded, which forms the contact or base surface of the milling insertagainst the shim plate 6. Peripherally outside the contact surface 18,chip surfaces 19 (see FIGS. 4 and 5) are formed, which together with theupper portions of the clearance surfaces 13, 15 delimit the differentcutting edges. In order to separate the clearance surfaces 13, 15adjacent to the active cutting edge 11 a from the other clearancesurfaces, the same have been provided with the suffix a in FIG. 4. Inthis connection, it should also be pointed out that the referencedesignations 12, 14 point at the cutting-edge lines formed in thetransitions between the clearance surfaces and the chip surfaces.

In the embodiment shown, not only the clearance surfaces 13, but alsothe clearance surfaces 15, extend perpendicularly to the reference planeRP (and are therefore also running parallel to the center axis C2).Because the effective setting angle κ of the milling inserts (see FIG.2) in this case should amount to approximately 45°, the pair-wiseco-operating secondary and main edges 14, 12 and the respectiveclearance surfaces 15, 13 connected to the same form an obtuse, nominalangle of 135° with each other as viewed in a planar view (see FIG. 6).Furthermore, the secondary edge 14 extends perpendicularly to a bisectorB, which in turn forms an angle of 45° with each pair of main edges 12and clearance surfaces 13 running toward a common, individual corner ofthe milling insert.

In FIG. 8, it is seen that the individual main edge 12 extends betweenfirst and second ends 20, 21 and has a total length designated L1. Fromthe first end 20, the main edge declines in the downward directionagainst the underside 16B of the milling insert, more precisely at anangle γ, in order to subsequently, from a lowest point 22, again risetoward the opposite second end 21. In FIGS. 8 and 9, P1 furtherdesignates a plane parallel to the reference plane RP.

As previously has been pointed out, the secondary edges of the knownmilling inserts are parallel to the neutral plane of the milling insertsand form the portions of the upperside and of the underside,respectively, situated highest or farthest from the neutral plane.

Reference is now made to FIGS. 10 and 11, which show how the individualsecondary edge 14 of the milling insert according to an embodiment ofthe invention is inclined at a moderate angle ε in relation to theneutral plane RP of the milling insert, more precisely in such a waythat a first end 23, which connects to the main edge 12, is situated ona lower level than the opposite, second end 24. In the example, theangle ε between the secondary edge and the neutral plane amounts to 3°.In this connection, it should be pointed out that the cutting edges 12,14 transform into each other via one or more radius transitions. In theexample, the radius transitions are shown in the form of two convex partsurfaces 25, 26 situated between the clearance surfaces 13, 15 of thecutting edges. As is clearly seen in FIG. 11, the described inclinationof the secondary edge 14 entails that the most exposed part of themilling insert, viz. the corner transition between the secondary edgeand the main edge, will lack the abrupt corner that will be the resultwhen the cutting edges—as viewed in side view—mutually form an anglebeing considerably smaller than 180°. More precisely, the secondary edge14 and the part edge 121 transform into each other along a substantiallystraight (or utmost slightly cambered) cutting-edge line as viewed fromthe side in the view according to FIG. 8. In other words, the twocutting-edge lines transform into each other along a harmonic transitionline, which strengthens the corner transition and imparts to the millinginsert an increased service life.

Here, it should be interposed that the plane P1 is orientated in such away that the uppermost end points 24 of all four secondary edges 14 arein the plane P1. In other words, the level of the plane P1 in relationto the neutral plane RP is determined by the axial distance between thesame and each end point 24.

Although ε in the example amounts to exactly 3°, this angle may varyprovided that it amounts to at least 1°. On the other hand, the angleshould not be more than 7°. Advantageously, the angle ε is within theinterval of 2°-5°.

To the naked eye, the secondary edge 14 appears as being straight, notonly in the planar views according to FIGS. 6 and 13, but also in theenlarged side view according to FIG. 11. However, in practice, thesecondary edge may have other shapes than truly linear, at least in oneof the co-ordinate directions. In particular, the same may be convexlyarched as viewed in planar view according to FIG. 13 and FIG. 13B. Insuch a way, the generated, plane surface of the piece to be machined canbe given an advantageous surface structure, which is illustrated in FIG.14. Instead of leaving diminutive, lowered chutes or ditches in thesurface, as is the case when the secondary edge is straight andtransforms into the main edge via a comparatively acute bump, diminutivecrests 27 invisible to the eye are formed between, in other respects,utmost slightly concave surface fields, which together are experiencedas a plane and smooth surface. It is also possible to give thecutting-edge line 14 a slightly convex shape as viewed in the side viewaccording to FIG. 11. In the last-mentioned case, the angle ε is definedby a chord extending between the end points 23 and 24 to the arc linethat constitutes the secondary edge.

Another significant difference between the milling insert according tothe present invention and the known milling inserts is that theborderline, along which the different cutting edges extend in the firstcase, is partially interrupted by non-chip-removing edge lines 28 (seeFIGS. 11-13), whereas the cutting edges of the known milling insertsextend along one single, continuous edge line for chip removal. In otherwords, all cutting edges transform directly into each other in the knownmilling inserts, while each individual main edge, e.g., the main edge 12d according to FIG. 4, ends at a certain distance from a neighboring,non-co-operating secondary edge 14 a, and is spaced-apart from the sameby the non-chip-removing edge line 28.

Inside the inactive edge line 28, a shoulder, in its entirety designated29, is formed, the top surface of which is designated 30. As is seen inFIGS. 8 and 9, the top surfaces 30 of all four shoulders 29 of themilling insert are situated in a common plane P2, which is situated on ahigher level than the plane P1, in which the highest end points 24 ofthe secondary edges 14 are situated.

In the shown, preferred embodiment, the top surface 30 of the shoulderis plane and extends inward from the outer edge line 28 flush with theclearance surface of the main edge, the same coinciding with the planeP2.

Reference is now made to FIG. 8, which illustrates the particularcontour shape that the main edge 12 has between the two ends 20, 21thereof. From the first end 20, a first part edge 121 extends up totransition point 31 at the beginning of an arched, second part edge 122,which forms a transition to a third part edge 123 that extends up to thepoint 22. The part edge 121 leans, as previously been pointed out, inrelation to the neutral plane RP at an angle γ that in the exampleamounts to 6°, while the third part edge 123 in this case issubstantially parallel to the neutral plane RP and forms the lowermostpart of the main edge. In the example, the two part edges 121 and 123are straight, although it is also possible to give one, or both, of thema slightly concave shape (or even a shape that may alternate betweenconcave, straight and/or convex). In this connection, it should bepointed out that it is, per se, possible to form also the third partedge 123 at a certain, moderate angle in relation to the neutral planeRP. In any event, the angle should, in such a case, be considerablysmaller than the angle γ. Although the angle γ in the example amounts to6°, the same may vary upward as well as downward. However, it shouldamount to at least 3° and at most 10°. The second part edge 122, servingas a transition between the two part edges 121, 123 has a concave shapeand in this case a radius R1 that amounts to 10 mm. The length L2 of thepart edge 121 is, as is clearly seen in FIG. 8, less than half of theentire length L1 of the main edge 12. In the example, L2 amounts toapprox. 36% of L1.

At the point 22, the part edge 123 transforms into a fourth part edge124, which, like the part edge 122, has a concave arc-shape, but acomparatively small radius R2 that in the example amounts to 1.5 mm. Thelength L4 of the part edge 123 amounts to approximately 38% of the totallength L1, while the length L3 amounts to approximately 12% of L1 and L5to 14% of L1. The length L6 of the secondary edge 14 (see FIG. 6)amounts, in the example, to approximately 23% of the total length L1 ofthe main edge. In practice, this value should be within the interval of15-35%, preferably 20-30%.

All above-mentioned measures relate to a concrete example of a millinginsert, the IC measure of which (see FIG. 6) amounts to 13 mm, themilling insert having a thickness T (see FIG. 7) of 5.1 mm. The measure“t” by which the part edge 123 is countersunk in relation to the planeP1 amounts, in the example, to 0.4 mm, i.e., approximately 8% of thethickness T. This value should be within the interval of 5-12%, suitably6-10%. It should also be pointed out that in this case, the diameter Dof the hole 17 amounts to 4.8 mm. In this connection, L2 amounts toapprox. 4 mm and L1 to 8.7 mm.

When the milling insert is used for fine milling (when the requirementof the surface finish is great) and the cutting depth is so great thatat most the entire length L2 of the part edge 121 is utilized, thenegative axial orientation of the cutting edge is reduced by γ°, i.e.,in the example by 6°. This means that the main edge becomescomparatively easy-cutting, when the cutting depth is limited and therequirement of the surface finish is great. If the milling insert wouldbe used for rough milling, the cutting depth may be so great that almostthe entire length L1 of the main edge is utilized. However, in roughmilling, the requirement of the surface finish is usually moderate ornon-existent. Therefore, it is incidental that the third part edge 123is parallel to the neutral plane RP. The advantage of locating the thirdpart edge 123 parallel to the neutral plane is that a great amount ofmaterial in the milling insert can be retained in comparison with thealternative that the first part edge 121 would slope all the way up to alowest point situated near the end 21, as is the case with the millinginsert according to U.S. Pat. No. 5,807,031. In other words, the millinginsert according to the present invention becomes stronger than themilling insert known by U.S. Pat. No. 5,807,031.

Inside the concave part edge 124, the chip surface 19 (see FIG. 12)forms a concavely arched surface 19 a, which transforms into a sidelimiting surface 32 on the shoulder 29. The surface 32 extends up to theplane top surface 30 and forms, together with the surface 19 a, aformation that may be compared to a “ski slope.” Inside the secondaryedge 14, the chip surface includes a plane part surface 19 b, whichleans downward at a fairly large angle (lacks designation) to the planebase surface 18 of the milling insert (see FIGS. 4, 9 and 12).

Although the cutting edges described above, per se, could be sharp,e.g., by grinding, in the preferred embodiment, the same are formed withso-called reinforcement bevels 33 (see FIGS. 4 and 5), i.e., utmostslender surfaces in the immediate connection with the respectiveclearance surfaces. In this context, it should also be mentioned thatthe milling insert may be direct-pressed in so far that it obtains thefinal shape thereof directly after pressing and sintering, and withoutneeding to be after-treated by grinding or the like.

As has previously been pointed out, the inclination of the secondaryedges of in the way described above entails that the most sensitiveportions of the milling insert, viz. the corner transitions between theco-operating secondary and main edges, are strengthened mostconsiderably. The inclination also means that the secondary edgesdecline downward from the shoulders serving as chip-hammeringprotection, whereby the same are less exposed to possible chips that maypass along the top surfaces of the shoulders. The fact that the topsurfaces of the shoulders are situated at a higher level than thehighest points of the secondary edges, decreases in addition the risk ofdamage to the secondary edges in connection with manufacture, handlingand the like, because the milling insert can rest on the shouldersinstead of the secondary edges. By terminating the initially decliningpart edge of the main edge at a limited distance from the co-operatingsecondary edge and let the same transform into a second part edgesubstantially parallel to the neutral plane, furthermore the advantageis gained that the cemented carbide material in the milling insert isnot unnecessarily reduced due to the desired inclination of the mainedge adjacent to the secondary edge. In such a way, the milling insertretains a good strength without the requirement of surface finish duringfine milling (when the cutting depth is smaller than half of theeffective length of the main edge) being neglected.

While the invention has been disclosed with reference to certainpreferred embodiments, numerous modifications, alterations, and changesto the described embodiments are possible without departing from thesphere and scope of the invention, as defined in the appended claims andtheir equivalents thereof. For example, the shape and location of thesecondary edges as well as of the shoulders may be varied within fairlywide limits. For instance, the top surface of the individual shouldermay, on one hand, be spaced apart a distance from the non-chip-removingborderline adjacent to the clearance surface of the main edge, and, onthe other hand, have other shapes than exactly plane, e.g., arched orhemisphere-like. Furthermore, the invention is applicable not only toface milling inserts, but also to end mill inserts. Although theinvention originates from problems that essentially relate todouble-sided face milling inserts, the particular insert geometry beingthe solution to the problems and presented above, is also applicable tosingle-sided milling inserts, i.e., milling inserts that include aseries of at least three cutting edges only along the upperside thereof,a plane underside forming a reference plane parallel to the upperside(in such cases, the underside may be formed with serrations or othertypes of coupling members). In other words, the invention should beconsidered to include not only double-sided milling inserts, but alsosingle-sided inserts having only one set of indexable cutting edges,having the unique geometry described above. It should also be mentionedthat the milling insert may be fixed by, e.g., clamps, wedges or thelike, wherein the milling insert does not require any hole. Also, thenumber of cutting edges along the upperside (and the underside,respectively) may vary all the way from three and upward. Accordingly,it is intended that the invention not be limited to the describedembodiments, but that it have the full scope defined by the language ofthe following claims.

What is claimed is:
 1. A milling insert, comprising: an upperside, anunderside, and a reference plane parallel to the upperside and theunderside; a plurality of indexable cutting edges formed along aperipheral borderline in transitions between at least the upperside anda number of clearance surfaces, the cutting edges including an activechip-removing main edge and an active surface-wiping secondary edgecooperating therewith during a milling operation, the active secondaryedge forming an obtuse angle with the active main edge as viewed inplanar view from the upperside, and the active main edge extendingacross over half of the width of the insert along the reference planefrom a side view facing the clearance surface corresponding to the mainedge; the active main edge, from a first end of the active main edgeadjacent to the active surface-wiping secondary edge, first decliningtoward the underside of the milling insert and then, from a lowest part,rising toward an opposite second end of the active main edge, whereinthe active secondary edge is inclined at an angle (ε) in relation to thereference plane as viewed perpendicularly to the clearance surface ofthe active surface-wiping secondary edge, such that a first end of theactive surface-wiping secondary edge connected to the active main edgeis situated on a lower level than the opposite, second end of the activesurface-wiping secondary edge, and wherein at the second end of eachmain edge and at the second end of a neighboring secondary edge, theborderline is interrupted by non-chip-removing edge lines inside whichshoulders are formed having top surfaces, which are located in a commonplane parallel to and situated on a higher level than a plane in whichthe second ends of the secondary edges are commonly situated.
 2. Themilling insert according to claim 1, wherein the angle (ε) amounts to atleast 1°.
 3. The milling insert according to claim 1, wherein the angle(ε) amounts to at most 7°.
 4. The milling insert according to claim 1,wherein the angle (ε) amounts to at least 2° and at most 5°.
 5. Themilling insert according to claim 1, wherein the secondary edge has aconvexly arched shape.
 6. The milling insert according to claim 1,wherein the top surface of the shoulders is plane.
 7. The milling insertaccording to claim 1, wherein the top surface extends inward from anouter edge line flush with the clearance surface of the main edge. 8.The milling insert according to claim 1, wherein insert is double-sided.9. The milling insert according to claim 1, wherein a first portion ofthe main edge closest to the secondary edge is inclined at a first angle(γ) in relation to the reference plane up to a breaking point adjacentto a second portion, the angle of which to the reference plane issmaller than the first angle, the breaking point being situated closerto the secondary edge than the second end of the main edge.
 10. Themilling insert according to claim 1, wherein the milling insert has fourcutting edges on each of the upperside and the underside, thesurface-wiping secondary edges being disposed at the corners of themilling insert.
 11. A milling insert, comprising: an upperside, anunderside, and a reference plane parallel to the upperside and theunderside; a plurality of indexable cutting edges formed along aperipheral borderline in transitions between at least the upperside anda number of clearance surfaces; each cutting edge including achip-removing main edge and a surface-wiping secondary edge, thesecondary edge forming an obtuse angle with the main edge as viewed inplanar view from the upperside, and the chip-removing main edgeextending across over half of the width of the insert along thereference plane from a side view facing the clearance surfacecorresponding to the main edge; the main edge, from a first end of themain edge adjacent to the secondary edge, first declining toward theunderside of the milling insert and then, from a lowest part, risingtoward an opposite second end of the main edge, wherein the secondaryedge is inclined at an angle (ε) in relation to the reference plane asviewed perpendicularly to the clearance surface of the secondary edge,such that a first end of the secondary edge connected to the main edgeis situated on a lower level than the opposite, second end of thesecondary edge, and wherein at the second end of each main edge and at asecond end of a neighboring secondary edge, the peripheral borderline isinterrupted by non-chip-removing edge lines inside from which shouldersare formed having top surfaces, which top surfaces are located in acommon plane parallel to and situated on a higher level than a plane inwhich the second ends of the secondary edges are commonly situated. 12.The milling insert according to claim 11, wherein the top surfaceextends inward from an outer edge line flush with the clearance surfaceof the main edge.
 13. The milling insert according to claim 11, whereinthe angle (ε) amounts to at least 2° and at most 5°.
 14. The millinginsert according to claim 11, wherein a length of the first portion ofthe main edge is less than half a total length of the main edge.
 15. Themilling insert according to claim 11, wherein a length of the surfacewiping secondary edge is within 20-30% of a total length of the mainedge.
 16. The milling insert according to claim 11, wherein the angle(ε) amounts to at least 1°.
 17. The milling insert according to claim11, wherein the angle (ε) amounts to at most 7°.
 18. The milling insertaccording to claim 11, wherein the secondary edge has a convexly archedshape.
 19. The milling insert according to claim 11, wherein insert isdouble-sided.
 20. The milling insert according to claim 11, wherein afirst portion of the main edge closest to the secondary edge is inclinedat a first angle (γ) in relation to the reference plane up to a breakingpoint adjacent to a second portion, the angle of which to the referenceplane is smaller than the first angle, the breaking point being situatedcloser to the secondary edge than the second end of the main edge.